Sieve Editor: Display human readable error message for script errors

[FlexW]

Thanks for the new sieve editor:) I encountered one minor problem.

Expected behavior

The new sieve editor should give you an easily understandable error message if your script contains errors.

Actual behavior

The editor just displays: Oh snap. Request failed with 500

[kesselb]

Errrr ;) You are right of course. I actually added code to forward the error message from the sieve backend to frontend. It seems that our error middleware removes the error when server does not run in debug mode 🙈

[ChristophWurst]

It seems that our error middleware removes the error when server does not run in debug mode

Ah! Because I had a validation error that was very helpful when I had a syntax error :)